Drive system for a group of machines

ABSTRACT

A drive system powering a group of machines each fitted with a rectifying unit, wherein the inputs of the control devices of the machines&#39; drive motors are interconnected by an electrical bus which implements a power exchange. The system enables swapping current from a power supply between motors of different machines.

BACKGROUND OF THE INVENTION

A. Field

The present invention relates to a drive system for a group of machineseach equipped with a drive motor connected by control devices to a DCpower source.

B. Related Art

Applying DC power to the drive motor(s) of a machine, for instance aweaving machine, is known. In this procedure AC power is converted by arectifying unit of the particular machine into DC. This DC is applied bycontrolled switching units to the weaving machine's drive motor. Saiddrive motor preferably shall be a switched reluctance motor. Preferablysuch a weaving machine also contains a capacitive energy bufferconnected to the output of the rectifying unit and to the input of theswitching units. As a result, the power output beyond the rectifyingunit may remain nearly constant even when the power applied to theweaving machine's main drive motor varies. The power applied to saidmain drive motor of a weaving machine varies according to a periodicmotion of said weaving machine because it contains components that aremoved in one or the other direction at predetermined times.

The above described drive system meets requirements for weaving. Howeverit is less than desirable for electrically decelerating the weavingmachine's main drive motor. For example, the main drive motor must bedecelerated to reduce its speed during weaving or to stop it. In such acase the energy buffer must store the energy released by electricallydecelerating the main motor. Therefore an energy buffer of high capacityand/or ability to tolerate high voltages will be required.

As regards rapidly operating weaving machines, it is nearly impossibleto store the total energy released during deceleration into an energybuffer. Either an energy buffer of very large capacity would be needed,or the energy buffer's voltage would be too high. To precludeexcessively high energy buffer voltages, it is known in the state of theart to couple a resistor in parallel with the energy buffer when saidbuffer's voltage becomes excessively high, whereby energy is removedfrom said buffer and converted into heat in said resistor. When the maindrive motor of a weaving machine must be frequently decelerated, therewill be danger that the resistor temperature will become excessive.Moreover the heat dissipated by such a resistor must be absorbed byair-conditioning equipment in the weaving room. This aspect againrequires expenditure of relative large amounts of energy.

BRIEF SUMMARY OF INVENTION

The objective of the present invention is to improve a drive system ofthe above cited kind.

This goal is attained in that the electrical power source inputs of thecontrol devices of the drive motors of a group of machines areinterconnected by electric lines in order to carry out power swapping.

The drive system of the invention offers the advantage that the portionof the energy which is released during deceleration by one of themachines of a group may be utilized by another machine in said group. Inthis case any installed energy buffer need absorb less energy and/or anyresistor used need not be switched onto said buffer.

In a preferred embodiment of the invention, each machine is fitted witha rectifying unit mounted between an AC power source and the inputs ofthe particular control devices of said machines. The inputs to thecontrol devices are interconnected, and the rectifying units maycooperate to apply that power, for instance, required to start or toaccelerate one of the machines.

In another preferred embodiment of the invention, one energy buffer isallocated to the inputs of the control devices of each machine. In thisway the size of the individual energy buffers may be reduced. Usingenergy buffers of lesser capacity offers the advantage that these shallcontain fewer pollutants. Because the energy buffers of the individualmachines may swap energy among one other, they operate in the form ofthe sum of their capacities. As a consequence of being connected to oneanother, the total capacity of all energy buffers also may be reduced.Furthermore the interconnection of the energy buffers allows drawing onthe energy stored in each of them to start or accelerate a machine. Inthe latter case the rectifying units are not required to apply the fullpower needed to start or accelerate a machine. Also, using onerectifying unit for each machine, it becomes feasible to keep the powersubstantially constant from each rectifying unit even when only asmaller energy buffer is used per machine.

In yet another embodiment of the invention, each machine is combinedwith a resistor connected by switching units to the input of itsrespective control device and/or its respective energy buffer. Whenenergy must be dissipated as heat, this heat can spread over theindividual, switched-on resistors.

In another embodiment of the present invention, one joint resistor isallocated to a group of machines and is connected by switching units tothe inputs of the control means. Said single resistor may be installedat a remote location, for instance outside the weaving room. In thismanner the heat dissipated by this resistor need not be absorbed by theweaving room's air-conditioning equipment.

In yet another embodiment of the present invention, one joint rectifyingunit is mounted between an AC source and the inputs of the controldevices of the machines. In this design the power may be applied in partor in whole through the joint rectifying unit which illustrativelyconverts AC into DC with very high efficiency.

In yet another embodiment of the present invention, an inverter ismounted between control devices of the machines of a group and an ACpower source. This inverter converting DC into AC allows feeding theenergy recovered during deceleration back into the AC power source.While a single inverter suffices for one group of machines, the invertermay be selected as a more elaborate and correspondingly costlierinverter for recuperating said energy instead of converting it into heatby means of simpler and more economical resistors.

In still another embodiment of the present invention, the inputs of thecontrol devices of the group's machines cooperate with one joint energybuffer.

Preferably the rectifying unit(s) shall each be fitted with asemiconductor forming a DC current at a defined source voltage.

In a preferred embodiment of the present invention, the group's machinesare weaving machines of which the main drive shafts preferably are eachdirectly coupled to the associated drive shafts of the drive motors.

DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention are elucidatedin the description below and in relation to the illustrative embodimentsshown ion the drawings.

FIG. 1 schematically shows a group of weaving machines equipped with adrive system of the invention, and

FIGS. 2–5 schematically shows variants of the drive system of theinvention applied to groups of machines.

DETAILED DESCRIPTION

The drive system 1 of FIG. 1 electrically powers a group of machines 2,3 and 4 from an AC power source 5. Illustratively the power source 5 isa conventional 380-volt power line at 50 Hz frequency. A rectifying unit6 is allocated to each machine 2, 3 and 4 converting the AC from thepower source 5 into DC. The rectifying units 6 each are connected to theinputs 7 of control devices 8 which apply DC to the particular drivemotors 9 of the machines 2, 3 and 4. Each machine 2, 3 and 4 contains atleast one component 10 driven in periodic motion, that is, moving in onedirection or the other at a given time or being raised or lowered at agiven time. The electric drive motor 9 of each of the machines 2, 3 and4 is correspondingly driven into periodic motion in that appropriatelypower having a periodic time-function shall be applied in a controlledmanner by means of the control devices 8 to the drive motor(s) 9. Inparticular the time-function of applied power is controlled in a mannersuch that the torque will be constant.

In this embodiment the drive motor 9 is a switchable reluctance motorand as a result the control devices 8 each are a switching unit. Eachmachine 2, 3, 4 is fitted with a control unit 11 applying to the controldevices 8 (switching units) certain control parameters retrieved from amemory whereby the power is applied in periodic manner to the reluctancemotor 9. In this process the switchable reluctance motors 9 arecontrolled according to the machine angular positions in a motion suchthat, by means of the control devices 8 (switching units), predeterminedwindings of the switchable reluctance motor 9 shall be coupled during apredetermined time interval to the output of the rectifying unit 6. Theabove term “motion” denotes the change in angular position of theswitchable reluctance motor 9. In particular this motion is matched tothe natural motion of the machine's components.

In the shown embodiment, the machines 2, 3 and 4 each are fitted with anangular-position detector 12 determining the angular position of themain drive shaft of the particular machine 2, 3 and 4. Theseangular-position detectors 12 of each machine 2, 3 and 4 are coupled tothe respective control units 11. In this manner the control devices 8(switching units) of each machine 2, 3 and 4 can be actuated as afunction of the signal from the associated angular-position detector 12displaying the angular position of the particular machine 2, 3 and 4.Also, it is possible to determine the angular positions of the machines2, 3 and 4 by determining the angular positions of the respective drivemotors 9. As shown in FIG. 1, the control units 11 of the particularmachines 2, 3 and 4 also may be connected to a central control unitwhich for instance is set up remotely from the machines 2, 3 and 4 andwhich is connected by a network link with the control units 11 of theindividual machines.

The patent document WO 98/31856 (see U.S. Pat. No. 6,247,503) disclosesa drive motor of which the drive shaft is directly connected to or evenis integral with the weaving machine's main drive shaft. The patentdocument WO 99/27426 (see U.S. Pat. No. 6,525,496) discloses how such adrive motor is powered into a specific motion, namely the power appliedto this drive motor is controlled as a function of the angular positionof said machine. This driving mode is preferred also with respect to themachines of a group that are driven by the drive system of theinvention. For these reasons the contents of the patent document U.S.Pat. No. 6,525,496 are hereby declared to be part of the presentapplication.

The electrical power source inputs 7 of the control devices 8 and hencethe outputs of the individual rectifying units 6 of the group ofmachines 2, 3 and 4 are interconnected by an electric line 14, as aresult of which DC can flow between the group's machines 2, 3 and 4 andalso may be swapped. Therefore the DC power of one of the rectifyingunits 6 may pass into the individual machines 2, 3 and 4 of the saidgroup to thereby optimize the power consumption of the motors of thegroup.

In a preferred embodiment of the invention, each rectifying unit 6comprises a number of semiconductors which may or may not be controlled,for instance a number of diodes which convert AC into DC with a definedpower source voltage. To avoid that one of the rectifying units 6 beexcessively loaded, advantageously rectifying units 6 are used that willsupply DC of substantially the same voltage. Therefore identicalrectifying units 6 will be preferably used for the individual machines2, 3, 4.

The electric line 14 shall be of sufficient diameter and therefore havesufficiently low impedance so that the power may be transmitted in nearlossless manner. With respect to weaving machines, such a line 14 shallsupply a power of at least 3 kW without being significantly andconstantly heated by that transmission. Illustratively lines of copperof several mm in diameters are appropriate.

In the embodiment of FIG. 1, each machine 2, 3 and 4 contains anelectrical energy buffer 15 mounted between the particular output of therectifying unit 6 and the input 7 of the associated control device 8.Each of said buffers 15 illustratively is in the form of a capacitorwhich may store and release energy. The energy contained in each energybuffer 15 may be fed to one of the drive motors 9 of one of the machines2, 3 or 4. The energy released when decelerating a drive motor 9 of oneof the machines 2, 3 or 4 also may be fed to one of the energy buffers15 still able to accept it. This energy storage is not restricted to oneenergy buffer mounted at one of the particular machines 2, 3 or 4.Consequently any one of the machines 2, 3 or 4 when required to applypeak power may draw energy from the energy buffers 15 and furthermorefrom the rectifying units 6 of each of the other machines.

The energy released during braking or during deceleration of aparticular machine may be fed to another machine of the same group, as aresult of which the energy buffer(s) 15 are not required to reabsorb theentirety of the said released energy and/or so that additional resistorsdissipating energy into heat will not be needed. This feature isappropriate foremost as regards weaving machines of which theoperational rate must be periodically reduced according to a givenpattern being woven. Illustratively such shall be the case when weavingin several colors, whereby a given filling must be woven at a lowerspeed. The energy stored in the energy buffers of such weaving machinesmust also be available in order to raise again the operational speed ofthe weaving machine. As regards a weaving machine of which theoperational speed varies according to a given pattern, for instancebetween 1,200 and 900 picks a minute, approximately 3 joules arereleased in deceleration. This released energy is partly stored in theenergy buffers 15 and is partly absorbed by the other machines.

The drive system of the invention only rarely is susceptible to the needof converting released energy into heat by connection to a resistor.However such a case may arise if several machines are to be stoppedsimultaneously. For the sake of safety and as shown in FIG. 2, aresistor 16 is provided for each machine 2, 3 and 4 and is connected byswitching units 17 to the outputs of the rectifying units 6 and to theinputs 7 of the control devices 8. In this manner each resistor 16 isalso connected to the energy buffers 15. The switching units 17 arecontrolled by the central control unit 13. All resistors 16 may beswitched ON in the event the voltage of the energy buffers 15 becomesexcessive. Such a voltage value is measured by a voltmeter 18 connectedto the control unit 13 and to the inputs 7 of the control devices 8.Furthermore temperature sensors hooked up to the control unit 13 may beassociated with the resistors 16. In that case and as a function of thetemperature of each resistor 16, the control unit 13 may switch ON theresistor 16 at the lowest temperature if the voltage across the energybuffers 15 is excessive.

Only one resistor 19 is allocated to the group of machines 2, 3 and 4 inthe embodiment mode shown in FIG. 3, and can be coupled by the switchingunit 20 with the inputs 7 of the control devices 8 of said machines 2, 3and 4. Appropriately this single resistor will be mounted outside theroom housing the machines 2, 3 and 4, in particular to avoid loading theair-conditioning equipment for that room. The embodiment mode of FIG. 3furthermore includes a joint rectifying unit 22 of which the output 21is connected to the line 14 which in turn is connected to the inputs 7of the control devices 8.

The basic design of FIG. 4 corresponds to that of FIG. 1. However itincludes furthermore an inverter 23 which upon voltages at the inputs 7of the control devices 8 being reached or exceeded, will convert DC intoAC that shall be fed into the AC power source 5. This inverter 23 isconfigured between the inputs 7 of the control devices 8 and the ACpower source 5. In such a design, the resistors 16 and/or 19 may beeliminated. As regards a drive system 1 of the invention, theeventuality of having to feed power back into the power source 5 isremote. Accordingly a relatively small inverter 23 may be used, that is,one which may be smaller than if each machine 2, 3, 4 were fitted withan inverter and required to feed back energy being released at thatmachine.

A joint energy buffer 24 in FIG. 4 replaces the previous individualenergy buffers 15 and is connected both to the inputs 7 of the controldevices 8 and to the outputs of the rectifying units 6.

The embodiment of FIG. 5 substantially corresponds to that of FIG. 3.However in this latter embodiment, the machines 2, 3 and 4 are notfitted with their own rectifying unit 6. Instead a centrally locatedrectifying unit 22 is connected between the AC power source 5 and theline 14. The output 21 of rectifying unit 22 is connected to the line 14connecting the inputs 7 of the control devices 8.

Obviously the invention is not restricted to a group of three machines2, 3, 4. At least two machines are needed. However the invention'sadvantages shall be greater the more machines belonging to one group areserviced by the drive system of the invention.

In the shown and above discussed embodiments, each machine 2, 3,4 isfitted with only one drive motor 9. However several drive motors may beused for each machine to drive specific components of that machine. Thepower applied from the power source to the individual drive motors maybe considered equivalent to one equivalent power applied to a singlefictitious drive motor of the particular machine.

The individual embodiments discussed above also may be combined withinthe scope of the present invention. Machines other than weaving machinesalso are applicable, that are powered and decelerated by a drive motor,for instance compressors equipped with an electric drive motor.

As regards the drive systems of FIGS. 1 through 4, the rectifying unitsand energy buffers of each machine may be designed for a physical sizefor an average applied power and for storage of average energy. Theyneed not be designed for storing energy peaks when a machine is beingdecelerated or to supply peak power when starting a machine. On accountof such a compact design, the electric efficiency of each rectifyingunit of the group of machines will be improved. The invention alsoallows limiting the fluctuations in the power to be applied by eachrectifying unit, and this feature also improves electrical efficiency.

The drive system of the present invention is especially appropriate fora group of machines of which the central control unit 13 contains meansdriving the electric drive motors 9 of the group machines 2, 3 and 4 inperiodic motions. In an especially advantageous manner, the periodicmotions of the individual machines 2, 3 4 of said group will be matchedto one another in a manner so as to limit the total power applied to thegroup of machines 2, 3, 4 at a predetermined limit. In that case saidvalue illustratively shall be a maximum value and/or a maximum change ofthe total applied power. The power applied to the drive motors 9 of theindividual machines 2, 3, 4 can be controlled in a way disclosed in thepatent document WO 99/27426 (U.S. Pat. No. 6,525,496), whereinadditionally the motions of the individual machines are matched to eachother, for instance by the central control unit 13, for instance beingphase-shifted. This feature can be implemented by controlling the mutualangular positions of the various machines. In other words, theparticular motion of one machine will be matched to the motions of theother machines in a way that the instant at which one machine absorbsmaximum power will not coincide with the instant at which anothermachine of the group also absorbs maximum power. As a result, the powerapplied by each rectifying unit may be kept nearly constant even whenusing a comparatively small energy buffer for each machine.

The invention offers the further advantage that a single machinetogether with its rectifying unit 6 and any energy buffer 15 and/or anyresistance 16 that might be associated to it will work well per se, but,on account of the line 14 in the group, will operate even moreefficiently. For that purpose and as regards the embodiments of FIGS. 1through 4, not only are lines provided for the AC power source 5 betweenthe individual machines, but also lines 14 for DC.

The invention also applies to a group of machines that are notdecelerated using electric drive motors. In that case the invention isadvantageous to start a machine, in particular if driven in periodicmotions.

However the drive system of the invention is especially appropriate forweaving machines. It allows improving electrical efficiency of a groupof weaving machines and therefore is substantially advantageous forweaving mills.

The apparatus of the invention is not restricted to the shown anddescribed embodiments. Further modifications may be resorted to withinthe scope of the invention.

1. A drive system comprising a group of separate weaving machines havingrespective components driven in periodic motion resulting in varyingpower consumption by each machine during each machine cycle, eachmachine including a drive motor connected by a control device to arectifier providing a DC power source from an AC power supply, eachdrive motor controlled and powered to deliver torque such that the powerrequired by each motor varies during a machine cycle, and wherein the DCpower source inputs of the control devices of the drive motors of themachines of said group are interconnected by electrical lines in amanner enabling swapping DC power source current by said electricallines whereby energy not required by a drive motor of one machine can beshifted to other drive motors of the other machines as needed tooptimize the total power consumption by said drive motors of allmachines.
 2. Drive system as claimed in claim 1, wherein each machinecontains a rectifying unit disposed between the AC supply and theelectrical power source input of the respective control device of eachsaid machines.
 3. Drive system as claimed in claim 1, wherein a singleenergy buffer is associated with each of the DC power source inputs ofthe control device of each one of said machines.
 4. Drive system asclaimed in claim 1, wherein a single joint rectifying unit is configuredbetween the AC power supply and the DC power inputs of the controldevices of the machines of the group.
 5. Drive system as claimed inclaim 1, wherein a single joint energy buffer is allocated to the DCpower source inputs of the control devices of the machines of the group.6. Drive system as claimed in claim 1, wherein each said at least onerectifier is fitted with a semiconductor forming a DC power supplyhaving a predetermined output voltage.
 7. Drive system as claimed inclaim 1, wherein the machines of said group are weaving machines. 8.Drive system as claimed in claim 1, wherein at least a main drive shaftof each weaving machine is directly connected to an output drive shaftof each respective drive motor.
 9. A drive system comprising a group ofmachines, each machine including a drive motor connected by a controldevice to a DC power source, wherein electrical power source inputs ofthe control devices of the drive motors of the machines of said groupare interconnected by electrical lines in a manner enabling swappingelectrical power source current by said electrical lines; and a jointresistor is associated with the group of machines and is connectedthrough a switching unit to the electrical power source inputs of thecontrol devices of the machines.
 10. A drive system comprising a groupof machines, each machine including a drive motor connected by a controldevice to a DC power source wherein electrical power source inputs ofthe control devices of the drive motors of the machines of said groupare interconnected by electrical lines in a manner enabling swappingelectrical power source current by said electrical lines; and aninverter is provided between the control devices of the machines of thegroup and an AC power source.
 11. A drive system comprising a group ofseparate machines, each machine including a drive motor connected by acontrol device to rectifier providing a DC power source from an AC powersupply, wherein electrical power source inputs of the control devices ofthe drive motors of the machines of said group are interconnected byelectrical lines in a manner enabling swapping electrical power sourcecurrent by said electrical lines; and wherein a joint resistor isassociated with the group of machines and is connected through aswitching unit to the electrical power source inputs of the controldevices of the machines.
 12. A drive system comprising a group ofseparate machines, each machine including a drive motor connected by acontrol device to rectifier providing a DC power source from an AC powersupply, wherein electrical power source inputs of the control devices ofthe drive motors of the machines of said group are interconnected byelectrical lines in a manner enabling swapping electrical power sourcecurrent by said electrical lines, wherein a single resistor isassociated with each machine and is connected through a switching unitto the electrical power source input of a respective control device anda respective energy buffer.
 13. A drive system comprising a group ofseparate machines, each machine including a drive motor connected by acontrol device to rectifier providing a DC power source from an AC powersupply, wherein electrical power source inputs of the control devices ofthe drive motors of the machines of said group are interconnected byelectrical lines in a manner enabling swapping electrical power sourcecurrent by said electrical lines, wherein a single resistor isassociated with each machine and is connected through a switching unitto a respective energy buffer.